1. Field of the Invention
The present invention relates to an organic thin film transistor (TFT) and a method of fabricating the same, and more particularly, to an organic TFT and a method of fabricating the same in which an organic semiconductor layer includes carbon nanotubes (CNTs) and an organic semiconductor material and provides enhanced charge mobility and switching speed.
2. Description of the Related Technology
Over the past 10 years, laborious research into materials and applications of organic thin film transistor (TFTs) has accompanied the development of low-cost electronic devices. In particular, an organic TFT disposed on a substrate costs far less to fabricate than an inorganic TFT. An organic TFT may go well with a low-temperature process and a flexible electronic device (e.g., a flexible flat panel display (FPD)). Above all, the organic TFT is highly applicable to flexible FPDs such as a flexible liquid crystal display (LCD) and a flexible organic light emitting display (OLED).
Recently, an organic thin layer having a pentacene structure has been used for organic TFTs. In the early stages of development, the pentacene organic thin layer was an organic semiconductor layer having a charge mobility of 9×10−3 cm2/V·sec and an on/off ratio of 1×105. Recently, it has been reported that a pentacene organic thin layer has a charge mobility of 2.1 to 3.3 cm2/V·sec and an on/off ratio of 2×107 to 1×109 which are about the same as those of an amorphous silicon (a-Si:H) TFT. The term, “on/off ratio,” as used herein, refers to a ratio of current-on to current-off in a pixel of an active matrix (AM)-type display device. The on/off ratio greatly affects the operations of pixels of a display device.
Carbon nanotubes (CNTs) have a low work function and exhibit a high electric field concentration effect because of its high aspect ratio. Thus, they have excellent electron-emitting characteristics. For this reason, extensive research has been conducted for the use of CNTs in field emission display devices. Recently, CNTs have been studied with the aim of using them in various devices such as semiconductor devices, fuel batteries, secondary batteries, compound materials, and capacitors.
As disclosed in Korean Patent Laid-Open Publication No. 2004-0072067, a solution of a pentacene derivative is obtained by causing a Diels-Alder reaction between pentacene and dienophile in an organic solvent. The solution of the pentacene derivative is pyrolyzed by heating the solution from room temperature to 200° C. Then, a pentacene thin layer is formed using a thermal evaporation process or a solution-based process such as a spin coating process, an ink-jet printing process, or a screen printing process.
Also, CNTs are reduced to powder through an arc-discharge process, a laser vaporization process, a plasma-enhanced chemical vapor deposition (PECVD) process, a thermal chemical vapor deposition (thermal CVD), a vapor phase growth process, an electrolysis process, or a flame synthesis process.
There are two main types of carbon nanotubes (CNTs): single-walled nanotubes and multi-walled nanotubes, based on the number of walls which constitute CNTs. In addition, CNTs may be a rope-type which is obtained by lumping single-walled nanotubes into several ropes. The classifications used herein are the same as those known in the industry.
In using CNTs for emission devices, CNT powder is first mixed with a paste, and then deposited on a substrate to form a CNT layer, using a spin coating process, an ink-jet printing process, or a screen printing process. Subsequently, the CNT layer is sintered so as to be cured.
The organic TFT is advantageously used in electronic paper and flexible FPDs, owing to its low fabrication cost. However, because the organic TFT is far inferior to a polycrystalline silicon (poly-Si) TFT in terms of charge mobility and switching speed, it cannot be easily applied to voltage-drive FPDs that require high charge mobility and switching speed.